The present invention relates to an RF coil (radio frequency coil) and a magnetic resonance imaging system, and particularly to a flat type RF coil and a magnetic resonance imaging system having such an RF coil.
In a magnetic resonance imaging (MRI) system, a target to be shot or imaged is carried in an internal bore of a magnet system, i.e., a bore or space in which a static magnetic field is formed. A gradient magnetic field and a high-frequency magnetic field are applied to produce a magnetic resonance signal within the target. A tomogram is produced (reconstructed) based on its received signal.
In a magnet system using permanent magnets for the purpose of generating a static magnetic field, a flat type RF coil is provided close to the pair of permanent magnets opposite to each other to thereby apply a high-frequency magnetic field.
As the flat type RF coil, one is used which has patterns for current passes such as shown in FIG. 1 by way example. As shown in the same drawing, the RF coil has a pair of main passes 26 and return passes 27 which connect these main passes in series so that the directions of currents flowing therethrough become identical.
In order to uniformize the distribution of an intensity distribution of a high-frequency magnetic field in an imaging space or volume, main passes respectively comprise two current passes 26a and 26b and 26axe2x80x2 and 26bxe2x80x2 connected in parallel as shown in FIG. 2 by way of example. The two current passes 26a and 26b and 26axe2x80x2 and 26bxe2x80x2 are placed in parallel with a predetermined interval held therebetween.
Uniformly or appropriately proportionally-distributed currents are passed through these two current passes 26a and 26b (26axe2x80x2 and 26bxe2x80x2) to thereby achieve the uniformization of the intensity distribution of the high-frequency magnetic field. The proportion of the currents is adjusted by selecting values of circuit parts such as capacitors inserted into the passes.
As another technique, as shown in FIG. 3 by way of example, each of main passes 26 is formed of a wide conductor and a high-frequency magnetic field is formed by a distributed current flowing therethrough.
Since each of circuit parts normally has an error allowed for its nominal value from the viewpoint of standards, the ratio in current between the two current passes must accurately be adjusted while the error is being corrected in the RF coil having the configuration shown in FIG. 2, and hence a great deal of working man-hours are required. Further, since an eddy current based on a gradient magnetic field flows in the broad conductor in the RF coil having the configuration shown in FIG. 3, a gradient magnetic field characteristic is degraded.
Therefore, an object of the present invention is to implement an RF coil easy to uniformize the strength of a magnetic field and a magnetic resonance imaging system having such an RF coil. Further, the implementation of an RF coil free of an eddy current developed due to a gradient magnetic field and a magnetic resonance imaging system having such an RF coil is an object.
(1) The invention according to one aspect, for solving the above problems is an RF coil which comprises a first current pass group including a plurality of linear current passes placed on a plane surface in parallel with one another, a second current pass group which includes a plurality of linear current passes parallel to one another and is placed on the plane surface in such a relationship as to have a mirror image parallel to the first current pass group, and a third current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the first and second current pass groups while bypassing the first and second current pass groups along the plane surface.
In the invention according to the present aspect, all the linear electrical passes are connected in series so that they are identical in current direction through the first and second current pass groups. Therefore, currents for all the linear electrical passes or main passes are rendered identical to one another without any adjustments. Therefore, the uniformity of a high-frequency magnetic field is uniquely determined according to the spatial arrangement of the linear electrical passes.
(2) The invention according to another aspect, for solving the above problems is an RF coil which comprises a first current pass group including a plurality of linear current passes placed on a first plane surface in parallel with one another, a second current pass group which includes a plurality of linear current passes parallel with one another and is placed on the first plane surface in such a relationship as to have a mirror image parallel to the first current pass group, a third current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the first and second current pass groups while bypassing the first and second current pass groups along the first plane surface, a fourth current pass group including a plurality of linear current passes which are placed on a second plane surface opposed in parallel with the first plane surface with a space interposed therebetween, so as to extend parallel to the direction of the current passes of the first current pass group, a fifth current pass group which includes a plurality of linear current passes parallel with one another and is placed on the second plane surface in such a relationship as to have a mirror image parallel to the fourth current pass group, and a sixth current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the fourth and fifth current pass groups while bypassing the fourth and fifth current pass groups along the second plane surface.
In the invention according to the present aspect, two RF coils each having the same configuration as the RF coil described in (1) are laid out in an opposing relationship with a space defined therebetween. Therefore, a composite high-frequency magnetic field can be, formed between the two.
(3) The invention according to a further aspect, for solving the above problems is an RF coil which comprises a first current pass group including a plurality of linear current passes placed on a first plane surface in parallel with one another, a second current pass group which includes a plurality of linear current passes parallel with one another and is placed on the first plane surface in such a relationship as to have a mirror image parallel to the first current pass group, a third current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the first and second current pass groups while bypassing the first and second current pass groups along the first plane surface, a seventh current pass group including a plurality of linear current passes which are placed on a third plane surface adjacent to the first plane surface and opposed in parallel therewith, so as to extend parallel to one another along the direction orthogonal to the direction of the current passes of the first current pass group, an eighth current pass group which includes a plurality of linear current passes parallel to one another and is placed on the third plane surface in such a relationship as to have a mirror image parallel to the seventh current pass group, and a ninth current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the seventh and eighth current pass groups while bypassing the seventh and eighth current pass groups along the third plane surface.
In the invention according to the present aspect, two RF coils each having the same configuration as the RF coil described in (1) are combined together so that main passes are made vertical to each other. It is therefore possible to form a high-frequency magnetic field according to a quadrature system.
(4) The invention according to a still further aspect, for solving the above problems is an RF coil which comprises a first current pass group including a plurality of linear current passes placed on a first plane surface in parallel with one another, a second current pass group which includes a plurality of linear current passes parallel with one another and is placed on the first plane surface in such a relationship as to have a mirror image parallel to the first current pass group, a third current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the first and second current pass groups while bypassing the first and second current pass groups along the first plane surface, a seventh current pass group including a plurality of linear current passes which are placed on a third plane surface adjacent to the first plane surface and opposed in parallel therewith, so as to extend parallel to one another along the direction orthogonal to the direction of the current passes of the first current pass group, an eighth current pass group which includes a plurality of linear current passes parallel to one another and is placed on the third plane surface in such a relationship as to have a mirror image parallel to the seventh current pass group, a ninth current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the seventh and eighth current pass groups while bypassing the seventh and eighth current pass groups along the third plane surface, a fourth current pass group including a plurality of linear current passes which are placed on a second plane surface opposed in parallel with the first plane surface with a space interposed therebetween, so as to extend parallel to the direction of the current passes of the first current pass group, a fifth current pass group which includes a plurality of linear current passes parallel with one another and is placed on the second plane surface in such a relationship as to have a mirror image parallel to the fourth current pass group, a sixth current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the fourth and fifth current pass groups while bypassing the fourth and fifth current pass groups along the second plane surface, a tenth current pass group including a plurality of linear current passes which are placed on a fourth plane surface adjacent to the second plane surface and opposed in parallel therewith, so as to extend parallel to one another along the direction orthogonal to the direction of the current passes of the fourth current pass group, an eleventh current pass group which includes a plurality of linear current passes parallel to one another and is placed on the fourth plane surface in such a relationship as to have a mirror image parallel to the tenth current pass group, and a twelfth current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the tenth and eleventh current pass groups while bypassing the tenth and eleventh current pass groups along the fourth plane surface.
In the invention according to the present aspect, two quadrature type RF coils each having the same configuration as the RF coil described in (3) are placed in an opposing relationship with a space defined therebetween. It is therefore possible to form a composite high-frequency magnetic field in the space defined therebetween.
(5) The invention according to a still further aspect, for achieving the above problems is a magnetic resonance imaging system for forming an image, based on magnetic resonance signals acquired using a static magnetic filed, a gradient magnetic field and a high-frequency magnetic field, which comprises an RF coil for generating the high-frequency magnetic field, including a first current pass group including a plurality of linear current passes placed on a plane surface in parallel with one another, a second current pass group which includes a plurality of linear current passes parallel to one another and is placed on the plane surface in such a relationship as to have a mirror image parallel to the first current pass group, and a third current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the first and second current pass groups while bypassing the first and second current pass groups along the plane surface.
In the invention according to the present aspect, as an RF coil for the generation of a high-frequency magnetic field, one is used wherein all the linear electrical passes are series-connected so as to become identical in current direction through the first and second current pass groups, and currents flowing through all the linear electrical passes, i.e., main passes are rendered identical without any adjustments. Therefore, the uniformity of a high-frequency magnetic field is uniquely determined according to the spatial arrangement of the linear electrical passes.
(6) The invention according to a still further aspect, for solving the above problems is a magnetic resonance imaging system for forming an image, based on magnetic resonance signals acquired using a static magnetic filed, a gradient magnetic field and a high-frequency magnetic field, which comprises an RF coil for generating the high-frequency magnetic field, including a first current pass group including a plurality of linear current passes placed on a first plane surface in parallel with one another, a second current pass group which includes a plurality of linear current passes parallel to one another and is placed on the first plane surface in such a relationship as to have a mirror image parallel to the first current pass group, a third current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the first and second current pass groups while bypassing the first and second current pass groups along the first plane surface, a fourth current pass group including a plurality of linear current passes which are placed on a second plane surface opposed in parallel with the first plane surface with a space interposed therebetween, so as to extend parallel to the direction of the current passes of the first current pass group, a fifth current pass group which includes a plurality of linear current passes parallel with one another and is placed on the second plane surface in such a relationship as to have a mirror image parallel to the fourth current pass group; and a sixth current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the fourth and fifth current pass groups while bypassing the fourth and fifth current pass groups along the second plane surface.
In the invention according to the present aspect, as RF coils for the generation of high-frequency magnetic fields, ones are used wherein two RF coils each having the same configuration as the RF coil described in (1) are placed in an opposing relationship with a space defined therebetween. It is therefore possible to form a composite high-frequency magnetic field in the space defined therebetween.
(7) The invention according to a still further aspect, for solving the above problems is a magnetic resonance imaging system for forming an image, based on magnetic resonance signals acquired using a static magnetic filed, a gradient magnetic field and a high-frequency magnetic field, which comprises an RF coil for generating the high-frequency magnetic field, including a first current pass group including a plurality of linear current passes placed on a first plane surface in parallel with one another, a second current pass group which includes a plurality of linear current passes parallel with one another and is placed on the first plane surface in such a relationship as to have a mirror image parallel to the first current pass group, a third current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the first and second current pass groups while bypassing the first and second current pass groups along the first plane surface, a seventh current pass group including a plurality of linear current passes which are placed on a third plane surface adjacent to the first plane surface and opposed in parallel therewith, so as to extend parallel to one another along the direction orthogonal to the direction of the current passes of the first current pass group, an eighth current pass group which includes a plurality of linear current passes parallel to one another and is placed on the third plane surface in such a relationship as to have a mirror image parallel to the seventh current pass group, and a ninth current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the seventh and eighth current pass groups while bypassing seventh and eighth current pass groups along the third plane surface.
In the invention according to the present aspect, as an RF coil for the generation of a high-frequency magnetic field, one, is used wherein two RF coils each having the same configuration as the RF coil described in (1) are combined together so that main passes are made vertical to each other. It is therefore possible to form a high-frequency magnetic field according to a quadrature system.
(8) The invention according to a still further aspect, for solving the above problems is a magnetic resonance imaging system for forming an image, based on magnetic resonance signals acquired using a static magnetic filed, a gradient magnetic field and a high-frequency magnetic field, which comprises an RF coil for generating the high-frequency magnetic field, including a first current pass group including a plurality of linear current passes placed on a first plane surface in parallel with one another, a second current pass group which includes a plurality of linear current passes parallel with one another and is placed on the first plane surface in such a relationship as to have a mirror image parallel to the first current pass group, a third current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the first and second current pass groups while bypassing the first and second current pass groups along the first plane surface, a seventh current pass group including a plurality of linear current passes which are placed on a third plane surface adjacent to the first plane surface and opposed in parallel therewith, so as to extend parallel to one another along the direction orthogonal to the direction of the current passes of the first current pass group, an eighth current pass group which includes a plurality of linear current passes parallel to one another and is placed on the third plane surface in such a relationship as to have a mirror image parallel to the seventh current pass group, a ninth current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the seventh and eighth current pass groups while bypassing the seventh and eighth current pass groups along the third plane surface, a fourth current pass group including a plurality of linear current passes which are placed on a second plane surface opposed in parallel with the first plane surface with a space interposed therebetween, so as to extend parallel to the direction of the current passes of the first current pass group, a fifth current pass group which includes a plurality of linear current passes parallel with one another and is placed on the second plane surface in such a relationship as to have a mirror image parallel to the fourth current pass group, a sixth current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the fourth and fifth current pass groups while bypassing the fourth and fifth current pass groups along the second plane surface, a tenth current pass group including a plurality of linear current passes which are placed on a fourth plane surface adjacent to the second plane surface and opposed in parallel therewith, so as to extend parallel to one another along the direction orthogonal to the direction of the current passes of the fourth current pass group, an eleventh current pass group which includes a plurality of linear current passes parallel to one another and is placed on the fourth plane surface in such a relationship as to have a mirror image parallel to the tenth current pass group, and a twelfth current pass group in which all the linear electrical passes are series-connected so as to be identical in current direction through both groups of the tenth and eleventh current pass groups while bypassing the tenth and eleventh current pass groups along the fourth plane surface.
In the invention according to the present aspect, as RF coils for the generation of high-frequency magnetic fields, ones are used wherein two quadrature type RF coils each having the same configuration as the RF coil described in (3) are placed in an opposing relationship with a space defined therebetween. It is therefore possible to form a composite high-frequency magnetic field in the space defined therebetween.
According to the present invention, an RF coil easy to uniformize the strength of a magnetic field and a magnetic resonance imaging system having such an RF coil can be implemented. Further, an RF coil which does not cause eddy currents due to a gradient magnetic field, and a magnetic resonance imaging system having such an RF coil can be implemented.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.